Magnetic fields affect the behavior of free radicals. The dominant process is a dramatic increase in the yield of radicals that escape from the triplet pair in the presence of EMF. This process can be easily observed in heterogeneous media like micelles where the lifetime of radical pairs is longer, and all reactants are confined in a small volume. In addition, a higher level of molecular arrangement in micelles, or in other molecular aggregates, may also be important factors. For modeling studies, radical pairs are most conveniently generated in photochemical reactions via electron transfer or energy transfer processes, or through the direct photolysis of appropriate substrates. It is of interest to find appropriate heterogeneous systems for photochemical generation of radical in the presence of EMF. We have already studied photosensitization in differently charged micelles, which is an elegant way to control energy transfer processes. We have extended our studies to larger and higher organized premicellar aggregates. Some of these aggregates show a free exciton transition, which indicates a high degree of molecular organization, and is promising for the control of electron transfer reactions by irradiation of the photosensitizer Rose Bengal. We will apply these systems to study first the reactions involving nitric oxide and nitric oxide adducts to an aci-nitro moiety. Nitric oxide is biologically important paramagnetic intermediate, and we have considerable experience with its detection by EPR. Concurrent with the development of photochemical models for radical production, we have set-up the necessary apparatus to observe the influence of EMF. This includes a laser flash photolysis system based on a Surelite II Nd:YAG laser and an OPO tunable light converter combined with a sensitive optical detection system. The cellular subcompartments (membranes, DNA, proteins, mitochondria, etc.) might function as "reaction vessels" for radicals that can be influenced by an externally applied magnetic field similar way as radicals in the molecular aggregates of detergent we are testing.